By Jenny Winder
What to look out for in the May night sky
Starwatchers have plenty to occupy themselves with this month. The Full Moon on May 6th will coincide with the peak of the Eta Aquarid meteor shower in the East, cutting down the zenithal hourly rate (ZHR) considerably from its usual 40 meteors per hour. New Moon will be on May 2oth and on May 26th the waxing crescent Moon will occult M67, an open cluster of stars in the constellation of Cancer.
Venus is nearing the Sun in preparation for the transit across its surface in early June, so the planet dips below the horizon shortly after sunset. If you are quick you will see Venus’ crescent phase grow in diameter as the month progresses, from 37 arcseconds at the start of May to 56 arcseconds at the close of the month. Now is also a good time to look for the elusive Ashen Light, a subtle glow on the unlit part of Venus, similar to earthshine seen on the Moon, but much fainter. This phenomenon was first described in 1643 but has never been verified. Many have claimed to see it, but many more have not. Nobody has been able to image it and nobody knows what causes it. Saturn is still a spectacular sight low toward the South in Virgo, with the rings well displayed and casting shadows on the surface of the planet, while the shadow cast by the planet onto the rings will grow more prominent with time.
Virgo still fills the Southern sky so take the opportunity to look at the Virgo Cluster of galaxies. There are as many as 2000 galaxies in this cluster which comprises the heart of the Virgo Supercluster, part of the Local Group of galaxies that includes our own Milky Way. The Cluster is made up of a mix of spirals and elliptical galaxies
The globular cluster M13 in Hercules lies high in the South, between the Summer sky’s two brightest stars: Arcturus in Boötes to the right & Vega in Lyra to the left. Hercules is easily recognised by its ‘Keystone’ asterism and M13 lies along side nearest to Arcturus.
To the right of Arcturus lies the small constellation of Coma Berenices, containing eight Messier objects including M53, another globular cluster of stars and the Black Eye Galaxy M64 with its distinctive dark band of dust that gives this spiral galaxy its name.
We are now entering the season of nocilucent clouds. Most of the time astronomers curse the sight of clouds for obscuring the stars but these clouds are eagerly awaited. At this time of year, between May and August the Sun remains close to the horizon and illuminates the layer of water ice that lies between 76 km and 85 km in the part of Earth’s atmosphere called the Mesosphere. The clouds appear as a fine veil of glowing blue filaments. Look low in the Northwest from 21:00 and 23:00 UT or between 01:00 and 03:00 UT low in the Northeastern sky.